1. Field of the Invention
The invention relates generally to delivery of a layered media stream, and more particularly to control of the number of layers within the media stream (i.e., a layer count of the media stream).
2. Description of the Related Art
In recent years, in access networks which allow terminals to connect to an IP (Internet Protocol) network, a data transfer rate has been increased irrespective of whether each access network is mobile or fixed.
Along with the rapidly increasing use of such access networks, realization of large-scale media delivery services has been discussed which use an NGN (New Generation Network) as a core network. Media delivery services have been expected to have high quality and high security, which can accommodate various types of media and media delivery fashions (e.g., business models) owing to the employment of the NGN.
For definitions, the “media delivery service” means a service which allows a user's terminal to receive a media stream from a media delivery server and simultaneously reconstruct or playback the media stream. The “media stream” means audio or video content data which is to be delivered continuously in real time.
Conventionally, for a terminal to receive a media stream and simultaneously reconstruct it, the terminal requires a high performance processor and a large capacity memory to be incorporated.
In contrast, there is a technique which allows a media delivery server to transmit a layered media stream (i.e., a media stream to which a layered coding scheme has been applied), so that a terminal can reconstruct the received media stream in a manner that accommodates the throughput or the processing speed and the memory capacity of the terminal.
For definitions, the “layered coding scheme” means a scheme of coding a media stream by dividing the media stream into a plurality of layers with different levels, to thereby generate separate sets of encoded data in a hierarchical structure.
In the first or bottom layer, a set of media data with a minimum or primitive level of resolution is coded, and, in the next layer, a separate set of media data with a resolution higher than that of the first layer, to thereby allow multi-layer coding (e.g., coding based on the profile and the level in an MPEG2). The layered coding is performed depending on types of media or various quality scales, such as audio/video, perceivable frequency ranges, resolutions, or color tones.
The total number (i.e., a maximum number) “N” of layers within a media stream is equal to one of an audio layer plus “M” of video layers. In an example in which the total number “N” is equal to 21 (twenty one), the total number “N” is equal to one of an audio layer plus 20 (twenty) of video layers, that is,N=1+M, or(21)=1+(20).
When the NGN is used for a media delivery service, the status of IP packet transmission (i.e., how good IP packet transmission is performed) is always measured in a network located between a transmitter and a receiver. When a media stream is received, if the degradation in quality (e.g., disruption or deterioration of sound or image) is caused, then a transfer resource or a transfer rate of the media stream in the IP network is controlled. This prevents degradation in quality of the IP packets.
There is a first conventional technique, as disclosed in, for example, Japanese Patent Application Publication No. 2004-135017, that allows a media delivery server to store a plurality of media streams which are to be transferred at respective different transfer rates, and that allows a terminal to select one of the different transfer rates.
There is also a second conventional technique, as disclosed in, for example, Japanese Patent Application Publication No. 2000-295276, that allows a terminal or a network system to control the transfer rate, depending on the type of a media access (i.e., the type of a MAC (Media Access Control) layer) used in an access network.
There is still also a third conventional technique, as disclosed in, for example, Japanese Patent Application Publication No. 2003-298677, that allows a terminal to transmit to a media delivery server the status of the degradation in quality of the received media data (i.e., how bad the quality is), and that allows the media delivery server to control the encoding rate or the transmission rate and transmit the media data accordingly.
This conventional technique allows a desired transfer rate of IP packets for delivery of media data to be estimated and controlled, based on the size of IP packets to be transmitted, the loss rate of the IP packets, and round trip delay measured between a terminal and a media delivery server.
There is yet also a fourth conventional technique, as disclosed in, for example, “Multi-Session Rate Control for Layered Video Multicast,” coauthored by Xue Li, Sanjoy Paul, and Mostafa H. Ammar, in Proc. SPIE Multimedia Computing and Networking, vol. 3654, San Jose, Calif., January 1999, pp. 175-189, that allows a terminal by itself to control the increase/decrease of the number of layers to be layered-coded, depending on the status of degradation in quality measured by a terminal on a reception side.
This technique allows each of terminals on a reception side, by itself, to ascertain the status of degradation in quality, and allows a successively selected one of the terminals in the same order in which the terminals successively start reception of media data, to acquire the resource of the transmission frequency band.
There is still yet also a fifth conventional technique, as disclosed in, for example, “Equation-based Layered Video Multicast with Explicit Congestion Notification,” coauthored by Kitae Nahm, Qing Li, and C.-C. Jay Kuo, in Proc. Global Telecommunications Conference, 2003, GLOBECOM '03, IEEE, vol. 6, pp. 3580-3584, that allows a transmission device on a transmission side to control, by its independent decision, the increase/decrease of the number of layers to be layered-coded.
When the first conventional technique is implemented, the transfer rate is selected by a terminal, according to only its independent decision, irrespective of whether the whole network is congested or not.
This results in a risk that the whole network can lose the quality of service in a large scale, with an additional risk that each terminal can increase the traffic congestion of the network for an elongated period, because of each terminal's independent selection of an I transfer rate.
When the second conventional technique is implemented for an individual terminal which uses selectively a plurality of access networks, there is a need to prepare different kinds of control schemes for respective access networks.
Additionally, this may make differences between the result of control based on layers lower than a MAC (Media Access Control) layer, and the quality of an IP application service, due to control of application layers such as packet loss compensation.
When the third conventional technique is implemented, the load of a media delivery server and the traffic congestion of the network may increase due to additional traffic for allowing a terminal to transmit to the media delivery server, information indicative of how much the quality of service has been degraded.
When the fourth conventional technique is implemented, terminals acquire the resource of the transmission frequency band in the same order in which the terminals successively start reception of media data, resulting in a failure to keep the terminals to be equal to each other with respect to the resources.
This allows each terminal to control the increase/decrease of the number of layers within a layered media stream (this control spends much time in, in particular, decreasing the number of layers), resulting in a degraded ability of the control to follow up changes in congestion level in the whole network.
When the fifth conventional technique is implemented, a transmission device requires communication with every reception device for achieving the goal.
In this technique, the transmission device principally performs rate control. For this reason, if a link between a multicast router and a transmission node acts as a bottleneck link among subnets that the transmission device belongs to, then the status of traffic congestion will become worse.
In addition, even if the fifth conventional technique is implemented in combination with the fourth conventional technique, there is a need to monitor and control the quality of individual streams. This also makes it more difficult for a communication node which concurrently executes a plurality of priority-based data transfer processes to ensure scalability in a filtering process.
In view of the foregoing, it would be desirable to control the number of layers within a media stream, based on a quality perceived by a user who is a viewer or listener at a terminal on a reception side, for allowing a media stream to be received with high quality irrespective of fluctuations in transmission quality of a network.